Chemical amplification type positive resist composition

ABSTRACT

A chemical amplification type positive resist composition is provided, comprising a resin which has at least one polymerization unit selected from a polymerization unit of 3-hydroxy-1-adamantyl acrylate and a polymerization unit of 3,5-dihydroxy-1-adamantyl (meth)acrylate, a polymerization unit of hydroxystyrene and a polymerization unit having a group uhstable to an acid, is itself insoluble or poorly soluble in an alkali but becomes alkali-soluble after said group unstable to an acid is dissociated by the action of an acid; and an acid generator, the composition being excellent in various abilities such as sensitivity, resolution, heat resistance, film retention ratio, applicability, exposure clearance, dry etching resistance and the like, particularly having further improved resolution and exposure clearance.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP01/02246 which has an Internationalfiling date of Mar. 21, 2001, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a resist composition suitable forlithography and the like acting by high energy radiation such as farultraviolet ray (including excimer laser and the like), electron beam, Xray and emitting light.

BACKGROUND ART

Recently, by increased integration of integrated circuits, submicronpattern formation is required. Particularly, lithography using excimerlaser from krypton fluoride (KrF) or argon fluoride (ArF) is paid toattention since it enables production of 64 M DRAM to 1 G DRAM. As theresist suitable for such excimer laser liphoraphy process, a so-calledchemical amplification type resist utilizing an acid catalyst and achemical amplification effect is being adopted. When a chemicalamplification type resist is used, an acid generated from an acidgenerator at irradiated part is diffused in the subsequent heattreatment (post exposure bake: hereinafter, abbreviated as PEB in somecases), and the solubility of the irradiated part in an alkali developeris changed by a reaction using the resulted acid as a catalyst, thus, apositive or negative pattern is obtained.

For providing a chemical amplification type positive resist,particularly, a positive resist for KrF excimer laser lithography, apoly(hydroxystyrene)-based resin in which a part of phenolic hydroxylgroups is protected by a group dissociating by the action of an acid isoften used in combination with an acid generator. As such a groupdissociating by the action of an acid, those forming an acetal type bondwith an oxygen atom derived from a phenolic hydroxyl group, for example,those having a structure in which tetrahydro-2-pyranyl,tetrahydro-2-furyl or 1-ethoxyethyl is bonded to an oxygen atom, arepaid to attention, from the standpoints of resolution, sensitivity andthe like. However, there is a limitation on resolution even if such aresin is used.

Further, in pattern formation by photolithography, in general, thefinished size of a resist pattern tends to vary depending on variationof exposure amount, and exposure latitude (also called exposure margin)is small. Thus, in conventionally known resist compositions, resolution,sensitivity, exposure clearance and the like are limited. Further, forproduction of an integrated circuit, dry etching is conducted using aresist pattern formed by photolithography as a mask. Therefore, theresist used in this is required to have also heat resistance and dryetching resistance.

The object of the present invention is to provide a chemicalamplification type positive resist composition excellent in variousabilities such as sensitivity, resolution, heat resistance, filmthickness after development at unexposed area, applicability, exposureclearance, dry etching resistance and the like, particularly, havingfurther improved resolution and exposure clearance.

The present inventors have intensively studied for attaining such anobject, and resultantly found that excellent abilities are obtained byusing at least one hydroxystyrene-based copolymer selected from3-hydroxy-1-adamantyl acrylate and 3,5-dihydroxy-1-adamantyl(meth)acrylate, as a resin component of a chemical amplification typepositive resist, completing the present invention.

SUMMARY OF THE INVENTION

Namely, the present invention provides a chemical amplification typepositive resist composition comprising a resin which has at least onepolymerization unit selected from a polymerization unit of3-hydroxy-1-adamantyl acrylate and a polymerization unit of3,5-dihydroxy-1-adamantyl (meth)acrylate, a polymerization unit ofhydroxystyrene, and a polymerization unit having a group unstable to anacid, and is itself insoluble or poorly soluble in an alkali but becomesalkali-soluble after the above-mentioned group unstable to an acid isdissociated by the action of an acid; and an acid generator.

The resin component which is a main component in the resist compositionof the present invention is itself insoluble or poorly soluble in analkali but becomes alkali-soluble by causing a chemical change by theaction of an acid, and has essentially at least two polymerizationunits; a polymerization unit of hydroxystyrene and at least onepolymerization unit selected from a polymerization unit of3-hydroxy-1-adamantyl acrylate and a polymerization unit of3,5-dihydroxy-1-adamantyl (meth)acrylate. These polymerization units areformed by opening of a double bond at a styrene part and a double bondat a (meth)acrylic acid part, and can be represented by the followingformulae (I) and (IIa) to (IIc), respectively

In a hydroxystyrene unit of the formula (I), a positional relationbetween a hydroxyl group and a vinyl group is not particularlyrestricted, however, p-hydroxystyrene is generally used.

Though this resin is itself insoluble or poorly soluble in an alkali, ithas a polymerization unit having a group unstable to an acid to becomealkali-soluble by causing a chemical change by the action of an acid.The group unstable to an acid is usually introduced in a resin, in theform of protection of an alkali-soluble group such as a hydroxyl group,carboxyl group and the like. As such a group unstable to an acid forprotecting an alkali-soluble group, specifically exemplified aretert-butyl, tert-butoxycarbonyl, acetal-based groups of the followingformula (III)

(wherein R¹ represents an alkyl having 1 to 4 carbon atoms, R²represents an alkyl having 1 to 6 carbon atoms or a cycloalkyl having 5to 7 carbon atoms, or R¹ and R² together form a trimethylene chain or atetramethylene chain), 2-alkyl-2-adamantyl of the following formula (IV)

(wherein, R³ represents an alkyl having 1 to 4 carbon atoms), and thelike. These groups shall be substituted for hydrogen on a hydroxyl groupor hydrogen on a carboxyl group.

Examples of the acetal-based group of the formula (III) suitably includetetrahydro-2-furyl, tetrahydro-2-pyranyl, 1-ethoxyethyl,1-isopropoxyethyl, 1-isobutoxyethyl, 1-ethoxypropyl,1-ethoxy-2-methylpropyl, 1-cyclohexyloxyethyl and the like, and of them,1-ethoxyethyl, 1-isobutoxyethyl, 1-isopropoxyethyl, 1-ethoxypropyl andthe like are preferable. Examples of the 2-alkyl-2-adamantyl of theformula (IV) include 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl and thelike.

In the above-mentioned groups unstable to an acid, tert-butoxycarbonylis usually substituted on a hydroxyl group, and 2-alkyl-2-adamantyl ofthe formula (IV) is usually substituted on a carboxyl group. Othertert-butyl and acetal-based groups of the formula (III) can besubstituted on any of a hydroxyl group and a carboxyl group.

The resist for KrF excimer laser exposure is generally in the form inwhich a group unstable to an acid protects a hydroxyl group in ahydroxystyrene unit, as describe above. Then, such a unit in which anacid-unstable group is bonded to a hydroxyl group in a hydroxystyreneunit can be represented by the following formula (V).

In the formula. Q represents a group unstable to an acid. As Q in thisformula, specifically listed are tert-butyl, tert-butoxycarbonyl,acetal-based groups of the above-mentioned formula (III), and the likeof them, acetal-based groups of the above-mentioned formula (III) arepreferable. In this preferable embodiment, the polymerization unit canbe represented by the following formula (VI).

In the formula, R¹ and R² are as defined previously in the formula(III). Of them, preferably, R¹ represents an alkyl having 1 to 4 carbonatoms and R² represent an alkyl having 1 to 6 carbon atoms or acycloalkyl having 5 to 7 carbon atoms, in the formula (III) or (VI).

The resin which has at least one polymerization unit selected from apolymerization unit of 3-hydroxy-1-adamantyl acrylate and apolymerization unit of 3,5-dihydroxy-1-adamantyl (meth)acrylate, apolymerization unit of hydroxystyrene and a polymerization unit having agroup unstable to an acid as described above can be produced asdescribed below, for example. First, when the group unstable to an acidis tert-butyl and it is substituted on a hydroxyl group inhydroxystyrene, tert-butoxystyrene and at least one selected from3-hydroxy-1-adamantyl acrylate and 3,5-dihydroxy-1-adamantyl(meth)acrylate are copolymerized according to an ordinary method, then,hydrolyzed appropriately to substitute a part of tert-butoxy groups by ahydroxyl group, thus, the above-mentioned cab be produced. Further, whenthe group unstable to an acid is tert-butoxycarbonyl and it issubstituted on a hydroxyl group in hydroxystyrene, a copolymer ofhydroxystyrene and at least one selected from 3-hydroxy-1-adamantylacrylate and 3,5-dihydroxy-1-adamantyl (meth)acrylate is reacted withdi-tert-butyl dicarbonate, thus, the above-mentioned cab be produced.

Next, when the group unstable to an acid is an acetal-based group of theabove-mentioned formula (III) and it is substituted on a hydroxyl groupin hydroxystyrene, a copolymer of hydroxystyrene and at least oneselected from 3-hydroxy-1-adamantyl acrylate and3,5-dihydroxy-1-adamantyl (meth)acrylate is reacted with an unsaturatedether compound of the following formula (IIIa)

(wherein, R² is as defined previously, R⁴ and R⁵ represent, mutuallyindependently, hydrogen or alkyl, and the total carbon number of them is0 to 3 or, R⁵ represents hydrogen, and R² and R⁴ together form atrimethylene chain or tetramethylene chain), thus, the above-mentionedcab be produced.

On the other hand, when the group unstable to an acid is tert-butyl,acetal-based group of the formula (III), 2-alkyl-2-adamantyl of theformula (IV) or the like and it is substituted on a carboxyl group,usually, an unsaturated compound in which such a group forms acarboxylate is copolymerized with hydroxystyrene and at least oneselected from 3-hydroxy-1-adamantyl acrylate and3,5-dihydroxy-1-adamantyl (meth)acrylate, thus, the above-mentioned cabbe produced. As the unsaturated compound in which a group unstable to anacid forms a carboxylate, listed are unsaturated aliphatic carboxylatessuch as acrylates and methacrylates, unsaturated alicyclic carboxylatessuch as norbornenecarboxylate, tricyclodecenecarboxylate,tetracyclodecenecarboxylate, and the like.

Copolymerization using hydroxystyrene or tert-butoxystyrene, and atleast one selected from 3-hydroxy-1-adamantyl acrylate and3,5-dihydroxy-1-adamantyl (meth)acrylate, and in some cases, further,monomers having a group unstable to an acid and/or other monomers, canbe conducted according to an ordinary method. For example, raw materialmonomers are dissolved in a suitable solvent, to this is added apolymerization initiator to initiate polymerization, and the reaction isallowed to continue under heat or heat removal. As the reaction solvent,alcohols such as methanol, ethanol, 2-propanol and tert-butanol,aromatic hydrocarbons such as benzene, toluene and xylene, ethers suchas tetrahydrofuran, 1,4-dioxane and the like can be used. As thepolymerization initiator, azo compounds such as2,2′-azobis(isobutyronitrile) and dimethyl 2,2′-azobis(2-methylpropionate), peroxides such as benzoyl peroxide and tert-butyl peroxide,redox-based initiators such as hydrogen peroxide/ferrous salt andbenzoyl peroxide/dimethylaniline, metal alkylated compounds such asbutyllithium and triethylaluminum, and the like can be used.

When tert-butoxystyrene is used as a raw material monomer, a copolymeris dissolved in a hydrophilic solvent, and heated under acidity, tohydrolyze a tert-butoxy group in the copolymer, obtaining a copolymercomprising at least one selected fromhydroxystyrene/3-hydroxy-1-adamantyl acrylate and3,5-dihydroxy-1-adamantyl (meth)acrylate. Further, when a group unstableto an acid is introduced in a copolymer comprising at least one selectedfrom hydroxystyrene/3-hydroxy-1-adamantyl acrylate and3,5-dihydroxy-1-adamantyl (meth)acrylate, an operation according to ausual protective group-introducing reaction may advantageously beconducted. For example, when an acetal-based group of theabove-mentioned formula (III) is introduced, a raw material copolymer isdissolved in a solvent, and an unsaturated ether compound of theabove-mentioned formula (IIIa) is reacted in the presence of an acidcatalyst, a part of hydroxyl groups in the copolymer can be changed toan acetal-based group of the above-mentioned formula (III). As the acidcatalyst in this reaction, inorganic acids such as hydrochloric acid andsulfuric acid, organic acids such as p-toluenesulfonic acid andcamphorsulfonic acid, and the like are used.

The resin component constituting the positive resist composition of thepresent invention essentially has, as described above, a polymerizationunit of hydroxystyrene, at least one polymerization unit selected from apolymerization unit of 3-hydroxy-1-adamantyl acrylate and apolymerization unit of 3,5-dihydroxy-1-adamantyl (meth)acrylate, and apolymerization unit having a group unstable to an acid. However, thisresin component may also contain various polymerization units such asstyrene, acrylonitrile, methyl methacrylate, methyl acrylate and thelike. Further, for improving transparency, it may be partiallyhydrogenated, or an alkyl group or alkoxy group and the like may beintroduced in a phenol nucleus. However, it is advantageous that thetotal amount of a polymerization unit of hydroxystyrene and at least onepolymerization unit selected from a polymerization unit of3-hydroxy-1-adamantyl acrylate and a polymerization unit of3,5-dihydroxy-1-adamantyl (meth)acrylate is 50 mol % or more of thewhole resin. The ratio of both polymerization units is usually in therange from 99:1 to 80:20, preferably in the range from 95:5 to 85:15, interms of molar ratio of hydroxystyrene unit: at least one polymerizationunit selected from a polymerization unit of 3-hydroxy-1-adamantylacrylate and a polymerization unit of 3,5-dihydroxy-1-adamantyl(meth)acrylate. The amount of a polymerization unit having a groupunstable to an acid is usually 50 mol % or less, preferably 10 mol % ormore and 45 mol % or less.

When a copolymer of hydroxystyrene/at least one selected from3-hydroxy-1-adamantyl acrylate and 3,5-dihydroxy-1-adamantyl(meth)acrylate is reacted with a compound for introducing anacid-unstable group, for example, di-tert-butyl dicarbonate or anunsaturated ether compound of the above-mentioned formula (IIIa), aprotective group can be introduced also on a hydroxyl group in at leastone selected from 3-hydroxy-1-adamantyl acrylate and3,5-dihydroxy-1-adamantyl (meth)acrylate, together with a hydroxyl groupin a hydroxystyrene unit. In the case of presence of such a group inwhich a hydroxyl group in at least one selected from3-hydroxy-1-adamantyl acrylate and 3,5-dihydroxy-1-adamantyl(meth)acrylate is protected with a group unstable to an acid, it isreasonable to think that this unit is included in polymerization unitshaving a group unstable to an acid.

Next, the acid generator which is another component in the positiveresist composition is a substance which is decomposed to generate anacid, by allowing radiation such as light, electron beam and the like toact on the substance itself or a resist composition containing thesubstance. An acid generated from an acid generator acts on theabove-mentioned resin, to dissociate a group unstable to an acid presentin the resin. Examples of such an acid generator include onium saltcompounds, s-triazine-based organic halogen compounds, sulfonecompounds, sulfonate compounds and the like. Specifically, the followingcompounds are listed.

Diphenyliodonium trifluoromethanesulfonate

4-methoxyphenylphenyliodonium hexafluoroantimonate,

4-methoxyphenylphenyliodonium trifluoroantimonate,

bis(4-tert-butylphenyl)iodonium tetrafluoroborate,

bis(4-tert-butylphenyl)iodonium hexafluorophosphate,

bis(4-tert-butylphenyl)iodonium hexafluoroantimonate,

bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate,

tripheylsulfonium hexafluorophosphate,

trlpheylsulfonium hexafluoroantimonate,

tripheylsulfonium trifluoromethanesulfonate,

4-methylphenyldiphenylsulfonium perfluorobutanesulfonate,

4-methylphenyldiphenylsulfonium perfluorooctanesulfonate,

4-methoxyphenyldiphenylsulfonium hexafluoroantimonate,

4-methoxyphenyldiphenylsulfonium trifluoromethanesulfonate,

p-tolyldiphenylsulfonium trifluoromethanesulfonate,

2,4,6-trimethylphenyldiphenylsulfonium trifluoromethanesulfonate,

4-tert-butylphenyldiphenylsulfonium trifluoromethanesulfonate,

4-phenylthiophenyldiphenylsulfonium hexafluorophosphate,

4-phenylthiophenyldiphenylsulfonium hexafluoroantimonate,

1-(2-naphthoylmethyl)thioranium hexafluoroantimonate,

1-(2-naphthoylmethyl)thioranium trifluoromethanesulfonate,

4-hydroxy-1-naphthyldimethylsulfonium hexafluoroantimonate,

4-hydroxy-1-naphthyldimethylsulfonium trifluoromethanesulfonate,

2-methyl-4,6-bis(trichloromethyl)-1,3,5-triazine,

2,4,6-tris(trichloromethyl)-1,3,5-triazine,

2-phenyl-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(4-chlorophenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(4-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(benzo[d][1,3]dioxolan-5-yl)-4,6-bis(trichloromethy 1)-1,3,5-triazine,

2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(3,4,5-trimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(3,4-dimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(2,4-dimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(2-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(4-butoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

2-(4-pentyloxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,

1-benzoyl-1-phenylmethyl p-toluenesulfonate (trivial name: benzointosylate),

2-benzoyl-2-hydroxy-2-phenylethyl p-tolueaesulfonate (trivial name:α-methylolbenzoin tosylate),

1,2,3-benzenetoluyl trismethanesulfonate,

2,6-dinitrobenzyl p-toluenesulfonate,

2-nitrobenzyl p-toluenesulfonate,

4-nitrobenzyl p-toluenesulfonate,

diphenyl disulfone, di-p-tolyl disulfone.

bis(phenylsulfonyl)diazomethane,

bis(4-chlorophenylsulfonyl)diazomethane,

bis(p-tolylsulfonyl)diazomethane,

bis (4-tert-butylphenylsulfonyl) diazomethane,

bis(2,4-xylylsulfonyl)diazomethane,

bis(cyclohexylsulfonyl)diazomethane,

(benzoyl)(phenylsufonyl)diazomethane,

N-(phenylsulfonyloxy)succinimide,

N-(trifluoromethylsulfonyloxy)succinimide,

N-(trifluoromethylsulfonyloxy)phthalimide,

N-(trifluoromethylsulfonyloxy)-5-norbornene-2,3-dicarboxyimide,

N-(trifluoromethylsulfonyloxy)naphthalimide,

N-(10-camphorsulfonyloxy)naphthalimide and the like.

It is generally known that, in a chemical amplification type positiveresist, by adding an organic base compound as a quencher, deteriorationin abilities due to deactivation of an acid by being left after exposurecan be improved, and also in the present invention, it is preferable tocompound an organic base compound, particularly, a nitrogen-containingbasic organic compound as a quencher. Specific examples of such anitrogen-containing basic organic compound include amines of thefollowing formulae.

In the formulae, R¹¹, R¹², R¹³, R¹⁴ and R¹⁵ represent each independentlyhydrogen, an alkyl, cycloalkyl, aryl or alkoxy optionally substituted bya hydroxyl group, and A represent an alkylene, carbonyl or imino. Here,the alkyl and alkoxy represented by R¹¹, to R¹⁵ can have about 1 to 6carbon atoms, and the cycloalkyl can have about 5 to 10 carbon atoms,and the aryl can have about 6 to 10 carbon atoms. The alkylenerepresented by A can have about 1 to 6 carbon atoms, and may be linearor branched. Further, a hindered amine compound having a hinderedpiperidine skeleton disclosed in JP-A No. 9-208864, which is a priorapplication of the applicant, can be used as a quencher.

The resist composition of the present invention preferably contains aresin component in an amount of 80 to 99.8% by weight and an acidgenerator in an amount of 0.1 to 20% by weight based on the total solidcontent. When a nitrogen-containing basic organic compound as a quencheris contained, it is preferably used in an amount of 10% by weight orless based on the total solid content in the resist composition. Thiscomposition can also contain a small amount various additives such as asensitizer, dissolution inhibitor, other resin, surfactant, stabilizer,dye and the like, if necessary.

The resist composition is usually used in the form of a resist solutioncontaining the above-mentioned components dissolved in a solvent, andapplied on a substrate such as a silicon wafer and the like according toan ordinary method such as spin coating and the like. The solvent hereinused may be one dissolving components, showing a suitable drying speed,and giving a uniform and smooth coated film after evaporation of asolvent, and can be one usually used in this field. Examples thereofinclude glycol ether esters such as ethylcellosolve acetate,methylcellosolve acetate and propylene glycol monomethyl ether acetate,esters such as ethyl lactate, butyl acetate, amyl acetate and ethylpyruvate, ketones such as acetone, methyl isobutyl ketone, 2-heptanoneand cyclohexanone, cyclic esters such as γ-butyrolactone, alcohols suchas 3-methoxy-1-butanol, and the like. These solvents can be used eachalone or in combination of two or more.

On a resist film applied on a substrate and dried, exposure treatmentfor patterning is performed, then, heating treatment for acceleratingde-protection group reaction (FEB) was conducted. Then, the film isdeveloped with an alkali developer. The alkali developer here used caninclude various alkaline aqueous solutions used in this field, andgenerally, aqueous solutions of tetramethylammonium hydroxide and(2-hydroxyethyl)trimethylammonium hydroxide (usually called: choline)are often used.

The present invention will be specifically illustrated by examplesbelow, but the scope of the present invention is not limited to theseexamples at all. In the examples, % and parts representing the contentor use amount are by weight unless otherwise stated. The weight-averagemolecular weight (Mw) and polydispersion (Mw/Mn) were measured by gelpermeation chromatography using polystyrene as a standard.

SYNTHESIS EXAMPLE 1 Production of Partial 1-ethoxyethylated Compound ofHydroxystyrene/3-hydroxy-1-adamantyl Acrylate Copolymer

(1) Production of hydroxystyrene/3-hydroxy-1-adamantyl AcrylateCopolymer

Into a flask was charged 92.8 g (0.53 mol) of 4-tert-butoxystyrene, 13.0g (0.06 mol) of 3 hydroxy-1-adamantyl acrylate, 52.9 g of methanol and105.8 g of 2-propanol, and they were refluxed under a nitrogenatmosphere at 75° C. Separately, 6.1 g of dimethyl2,2′-azobis(2-methylpropionate) was dissolved in 17.6 g of 2-propanol toprepare a solution which was dropped into the above-mentioned monomersolution kept at 75° C. over 30 minutes, then, the resulted mixture wasrefluxed itself for 8 hours. To this was further added 193.9 g of2-propanol, and the resulted mixture was refluxed again at 75° C. Intothis solution was dropped a mixed solution of 18.3 g of 36% hydrochloricacid and 18.3 g of 2-propanol. Subsequently, the mixture was refluxedfor 4 hours at the same temperature to cause hydrolysis, then, thesolution was cooled to room temperature. To this reaction mass was added528.9 g of n-heptane, and the lower resin layer was removed. This resinlayer was dissolved in 52.9 g of acetone, and 528.9 g of n-heptane wasadded, and the lower resin layer was removed again. The resulted resinlayer was dissolved in 634.7 g of methyl isobutyl ketone, and 211.6 g ofion exchanged water was added to this and the mixture was stirred andallowed to stand still, then, the organic layer part was removed.Further, an operation of addition of 211.6 g of ion exchanged water,stirring and separation was repeated four times. This organic layer wasdistilled under reduced pressure until the solution amount afterdistillation was 230.8 g under conditions of a temperature of 60° C. anda pressure of 80 Torr or less, and dehydrated azeotropically, to obtaina methyl isobutyl ketone solution of a copolymer of 4-hydroxystyrene and3-hydroxy-1-adamantyl acrylate. The solid concentration of the resultedresin solution was 26.3%, and this copolymer had a weight-averagemolecular weight of 11400 and a polydispersity of 1.77.

(2) Partial 1-ethoxyethylation of hydroxystyrene/3-hydroxy-1-adamantylAcrylate copolymer

Into a nitrogen-purged flask was charged 115.4 g (resin content: 30.4 g)of the methyl isobutyl ketone solution of a copolymer of4-hydroxystyrene and 3-hydroxy-1-adamantyl acrylate obtained in theabove-mentioned process (1) and 97.1 g of methyl isobutyl ketone, andthey were dissolved. To this 4 as added 4 mg (0.02 mmol) ofp-toluenesulfonic acid monohydrate, then, 8.68 g (0.12 mol) of ethylvinyl ether was dropped, further, they were reacted for 3 hours at 25°C. To this reaction solution was added 60 ml of ion exchanged water andthe mixture was stirred and allowed to stand still, then, the organiclayer part was removed. Further, an operation of addition of 60 ml ofion exchanged water, stirring and separation was repeated four times.The solvent was distilled off from this organic layer for concentration,then, propylene glycol monomethyl acetate was added and the solvent wasfurther distilled off, to cause solvent substitution. The resulted resinsolution had a solid concentration of 27.6%, and this resin was analyzedby ¹H-NMR to observe clearly a peak corresponding to a 1-ethoxyethoxygroup, and the ratio of the number of a 1-ethoxyethoxy group to thenumber of a benzene ring was 38.0%. Therefore, this resin is a substancein which hydroxyl groups in a copolymer of 4-hydroxystyrene and3-hydroxy-1-adamantyl acrylate are partially 1-ethoxy ethyl etherified.This resin is called resin A.

SYNTHESIS EXAMPLE 2 Production of Another Partial 1-ethoxyethylatedCompound of hydroxystyrene/3-hydroxy-1-adamantyl Acrylate Copolymer

The procedure in the process (2) in Synthesis Example 1 was repeatedexcept that the charging amount of ethyl vinyl ether was 5.45 g (0.08mol). The resulted resin solution had a solid concentration of 25.9%,and this resin was analyzed by ¹H-NMR to find that the ratio of thenumber of a 1-ethoxyethoxy group to the number of a benzene ring was20.5%. This resin is called resin B.

SYNTHESIS EXAMPLE 3 Production of Partial 1-ethoxyethylated Compound ofPolyhydroxystyrene

Into a 1 liter eggplant form flask was charged 40 g ofpoly(p-hydroxystyrene) (tradename: “VP-15000”)manufactured by NipponSoda Co., Ltd. (333 mmol as p-hydroxystyrene unit) and 47 mg (0.25 mmol)of p-toluenesulfonic acid monohydrate, and these were dissolved in 720 gof propylene glycol monomethyl ether acetate. This solution wasdistilled under reduced pressure under conditions of a temperature of60° C. and a pressure of 10 Torr or less, to cause azeotropicdehydration. The solution after distillation had a weight of 337 g. Thissolution was moved into a nitrogen-purged 500 ml four-necked flask, andinto this was added 12.0 g (166 mmol) of ethyl vinyl ether dropwise,then, they were reacted at 25° C. for 5 hours. To this reaction solutionwas added 62.3 g of propylene glycol monomethyl ether acetate and 320 gof methyl isobutyl ketone, further, 240 ml of ion exchanged water wasadded to this, and the mixture was stirred. Then, the mixture wasallowed to stand still, and the organic layer part was removed. To thisorganic layer was added again 240 ml of ion exchanged water, and themixture was stirred and allowed the stand still, and separated, toperform washing. Washing with ion exchanged water and separation wererepeated once more, then, the organic layer was removed and distilledunder reduced pressure, to remove water and methyl isobutyl ketone byazeotrope with propylene glycol monomethyl ether acetate, to give apropylene glycol monomethyl other acetate solution. The resulted liquidis a solution of a resin in which hydroxyl groups inpoly(p-hydroxystyrene) are partially 1-ethoxy ethyl etherified. Thisresin was analyzed by ¹H-NMR to find that 40% of hydroxyl groups hadbeen 1-ethoxy ethyl etherified. This resin is called resin C.

EXAMPLES 1, 2 AND COMPARATIVE EXAMPLE 1

In Example 1, the resin A is used, in Example 2, the resin A and theresin B were mixed at a solid content ratio of 1:1 before use, and inComparative Example 1, the resin C was used. These resins were dissolvedin admixture with an acid generator, quencher and solvent at thefollowing formulation, further, filtrated through a fluorine resinfilter having a pore diameter of 0.2 μm, to prepare resist solutions.

Resin (solid content) 10 parts Acid generator: 0.4 parts(bis(cyclohexylsulfonyl)diazomethane [“DAM-301” manufactured by MidoriKagaku K.K.]) Quencher: dicyclohexylmethylamine 0.015 parts Solvent: 50parts * (propylene glycol monomethyl ether acetate) * solvent amountincludes which introduced from resin solution

On a silicon wafer, the above-mentioned resin solution was spin-coated,then, pre-baked on a direct hot plate under conditions of 90° C. and 60seconds, to form a resist film having a thickness of 0.72 μm. The waferon which a resist film was thus formed was exposed through masks havingvarious forms and dimensions using KrF excimer stepper [“NSR 2205EX12B”manufactured by Nikon Corp., NA=0.55]. Then, PEB was conducted underconditions of 100° C. and 60 seconds on a hot plate, further, puddledevelopment was conducted with a 2.38% tetramethylammonium hydroxideaqueous solution. The pattern after development was observed by ascanning electron microscope, and sensitivity, exposure clearance andresolution were measured as described below, and the results are shownin Table 1.

-   Dose to clear sensitivity: It is represented by the minimum exposure    amount necessary to just clear the resist film in 1 mm square open    field. This is called Eth.-   Effective sensitivity(Dose to size): It is represented by the    exposure amount at which 0.25 μm line and space pattern is 1:1. This    is called E₀.-   Exposure latitude: It is represented by the value of E₀/Eth. When    this value is larger, the range from the exposure amount to clear    resist film to the standard exposure amount (dose to size) is wider,    and resist clearance error does not occur easily, and even if the    exposure amount is somewhat irregular, approximately constant    pattern dimension is imparted. Consequently, the exposure latitude    is better.-   Resolution: It is represented by the minimum dimension of line and    space pattern separating at the exposure amount at the effective    sensitivity.

TABLE 1 Sensitivity Exposure (mJ/cm²) clearance Resolution Example No.Resin Eth E₀ E₀/Eth (μm) Example 1 A 16 50 3.0 0.16 Example 2 A/B = 1/116 34 2.1 0.18 (weight ratio) Comparative C 15 29 1.9 0.22 Example

A resist composition prepared by using a resin having at leastpolymerization unit selected from hydroxystyrene/3-hydroxy-1-adamantylacrylate and 3,5-dihydroxy-1-adamantyl (meth)acrylate according to thepresent invention has improved exposure clearance and resolution.Further, various abilities such as sensitivity, heat resistance, filmretention ratio, applicability, dry etching resistance and the like canalso be maintained at excellent levels. Therefore, by using of thiscomposition, a fine resist pattern can be formed precisely.

1. A chemical amplification type positive resist composition comprisinga resin which has, at least one polymerization unit selected from apolymerization unit of 3-hydroxy-1-adamantyl acrylate and apolymerization unit of 3,5-dihydroxy-1-adamantyl (meth)acrylate, apolymerization unit of hydroxystyrene, and a polymerization unit havinga group unstable to an acid, and is itself insoluble or poorly solublein an alkali but becomes alkali-soluble after the above-mentioned groupunstable to an acid is dissociated by the action of an acid: and an acidgenerator.
 2. The composition according to claim 1 wherein thepolymerization unit having a group unstable to an acid is represented bythe formula (V)

wherein, Q represents a group unstable to an acid.
 3. The compositionaccording to claim 2 wherein the group Q unstable to an acid istert-butyl, tert-butoxycarbonyl or a group of the formula (III)

wherein, R¹ represents an alkyl having 1 to 4 carbon atoms, R²represents an alkyl having 1 to 6 carbon atoms or a cycloalkyl having 5to 7 carbon atoms, or R¹ and R² together form a trimethylene chain or atetramethylene chain.
 4. The composition according to claim 3 whereinthe group Q unstable to an acid is represented by the formula (III) inwhich R¹ represents an alkyl having 1 to 4 carbon atoms and R²represents an alkyl having 1 to 6 carbon atoms or a cycloalkyl having 5to 7 carbon atoms.
 5. The composition according claim 1 wherein thetotal amount of at least one polymerization unit selected from apolymerization unit of 3-hydroxy-1-adamantyl acrylate and apolymerization unit of 3,5-dihydroxy-1-adamantyl (meth)acrylate and apolymerization unit of hydroxystyrene is 50% or more based on the wholeresin.
 6. The composition according to claim 1 wherein at least onepolymerization unit selected from a polymerization unit of3-hydroxy-1-adamantyl acrylate and a polymerization unit of3,5-dihydroxy-1-adamantyl (meth)acrylate and a polymerization unit ofhydroxystyrene are present at a molar ratio of 1:99 to 20:80.
 7. Thecomposition according to claim 1 wherein the composition contains 80 to99.8% by weight of the resin and 0.1 to 20% by weight of the acidgenerator based on the total solid content in the composition.
 8. Thecomposition according to claim 1 which further contains anitrogen-containing basic organic compound as a quencher.
 9. Thecomposition according to claim 1 wherein the resin is obtained bycopolymerizing a compound of the formula (VII), hydroxystyrene and atleast one compound selected from the group consisting of3-hydroxy-1-adamantyl acrylate and 3,5-dihydroxy-1-adamantyl (meth)acrylate

wherein Q² in formula (VII) represents tert-butyl, group of the formula(III) or a group of the formula (IV),

wherein R¹ in formula (III) represents an alkyl having 1 to 4 carbonatoms, R² in formula (III) re resent an alkyl havin 1 to 6 carbon atomsor a cycloalkyl havin 5 to 7 carbon atoms, or R¹ and R² to ether form atrimethylene chain or a tetramethylene chain,

wherein R³ in formula (IV) represents an alkyl having 1 to 4 carbonatoms; and R⁴ in formula (VII) represents a hydrogen or methyl.